This invention relates to a diffuser for introducing gas in the form of bubbles into liquid held in an aeration basin, and more particular to so-called "disc" type diffusers having a bubble generating member of generally disc shape.
Diffusers for aeration basins holding a bio-degradeable liquid such as sewage are typically mounted at regularly spaced intervals on a grid of piping covering the bottom of the aeration basin. The piping delivers gas (usually air) under pressure to the diffusers, and each of the diffusers in turn generate relatively small bubbles in the liquid. Thus, air is delivered to the liquid in the basin in the form of small bubbles throughout the extent of the basin to enhance the transfer of oxygen to the liquid for faster oxidation treatment of the liquid.
Conventional "disc" type diffusers comprise a body member mounted on the piping and a disc of gas permeable ceramic material secured to the body member. The body member has a gas inlet at the bottom thereof adapted to receive air under pressure from the piping and a generally circular open top in flow communication with the gas inlet. The disc of ceramic material is fitted over the top of the body member in sealing relationship therewith. When air pressure is delivered to the diffuser, it flows into the inlet, up toward the top of the body member and out through the gas permeable ceramic disc into the sewage in the form of bubbles. Flow of liquid back down into the diffuser, when air under pressure is not being delivered, is blocked by the ceramic disc which is impermeable to the flow of liquid therethrough.
A problem with the conventional "disc" type diffuser is that over time suspended solids in the liquid being treated tend to deposit on the ceramic disc and block the gas passages or pores in the disc. This blockage tends to reduce the flow rate of air through the disc thereby reducing the amount of oxygen delivered to the liquid for treating the liquid. In the extreme, this blockage stops all flow of gas through the ceramic disc, thus rendering the diffuser incapable of performing its intended purpose. In addition, with the ceramic disc completely blocked, the air pressure may become so great as to cause the disc to be blown off the body member, thus also rendering the diffuser incapable of performing its intended purpose. In addition, the latter occurence allows liquid to enter the piping system, which may damage it.